1. Field of the Invention
The present invention relates to a starting motor which transmits rotation from an armature shaft of a d.c. motor to an output shaft, transmits the rotation of the output shaft to a pinion through an overrunning clutch, and starts an engine.
2. Description of the Prior Art
In FIG. 4, there is shown a cross sectional view of the essential parts of a conventional starting motor. A d.c. motor 1 has an armature shaft 2 extended from an armature, and the armature shaft 2 has a front end part provided with a sun gear 2a, which is constituted by a small gear. Reference numeral 3 designates a yoke which has field poles (not shown) mounted thereto. Reference numeral 4 designates an intermediate bracket which supports a front part side of the armature shaft 2 through a bearing 5. Reference numeral 6 designates a front bracket which is coupled to the yoke 3 through the intermediate bracket 4.
Reference numeral 7 designates an output shaft which is arranged at a front end of the armature shaft 2 through a steel ball 11 to be coaxial with the armature shaft 2, and which has an intermediate part provided with a helical spline 8. The output shaft has a clutch outer stopper 10 formed thereon before the helical spline 8 through an annular groove 9. The helical spline 8 has a plurality of tooth spaces 8a formed therein at equal pitches in the circumferential direction. There is formed a single through tooth space 8b between every adjoining tooth space 8a. The stopper 10 has through cutouts 10a formed therein to correspond to the through tooth spaces 8b. The output shaft 7 has a recess of thread portion 7b provided thereon behind the helical spline 8 to have a small diameter.
Reference numeral 13 designates a planetary reduction gear which is constituted as follows: Reference numeral 14 designates a plurality of planetary gears which mate with the sun gear 2a, and which are supported by supporting pins 15 through bearings 16. The supporting pins 15 are fixed to a carrier 7a which is formed by a flange at a rear end of the output shaft 7. Reference numeral 17 designates an internal gear frame which is fixed in the front bracket 6, and which has an inner periphery formed with internal teeth 17a, the internal teeth causing the planetary gears 14 meshed therewith to revolve. The internal gear frame 17 has a front end inner periphery supporting the output shaft at its rear end part through a bearing 18.
Reference numeral 20 designates an overrunning clutch which is carried on the output shaft 7, and which is constituted as follows: Reference numeral 21 designates a clutch outer member which has helical spline threads 21a formed thereon to engage with the tooth spaces 8a of the helical spline 8 on the output shaft 7. Reference numeral 22 designates a clutch inner member which transmits one-way rotation to the clutch outer member 21 through rollers 23, which is supported by the front bracket 6 through a bearing 24 and which supports the output shaft 7 through a bearing 25. Reference numeral 26 designates an engagement ring which is fitted into a rear end outer periphery of the clutch outer member 21. Between the engagement ring and the rear end of an enlarged portion of the clutch outer member, there is formed an annular engagement groove 21b. Reference numeral 27 designates a retaining ring which is fitted in the output shaft 7 to receive the clutch outer member 21 at a predetermined position when the clutch outer member 21 moves backward, and which is constituted by an E-shaped retaining ring.
Reference numeral 28 designates a pinion which is carried on a front end of the clutch inner member 22 by spline connection, which has a front end held by a stopper 29, and which is urged in a forward direction by a compression spring 30.
Reference numeral 31 designates an electromagnetic switch which is mounted on the front bracket 6, which has a plunger 32 forming a movable core, and which has a hook 33 inserted in and supported by the plunger 32 so that the hook 33 has a front end projected. Reference numeral 34 designates a shift lever which has a two-pronged upper end engaged with the hook 33, which has a two-pronged lower end engaged with the annular engagement groove 21b of the overrunning clutch 20 in an axial direction, and which is supported by the front bracket 6 at an intermediate projection 34a to be turnable, using the intermediate projection 34a as a fulcrum. Reference numeral 35 designates a rubber caulk which is fitted in a cutout of the front bracket 6.
Mounting the overrunning clutch 20 to the output shaft 7 is as follows: The helical spline threads 21a of the clutch outer member 21 of the overrunning clutch 20 which has been assembled is passed through the through cutouts 10a of the stopper 10, and through the tooth spaces 8b of the helical spline 8 until the threads 21a has reached the recess 7b of the thread portion. The clutch outer member 21 is turned by a half pitch of the threads 21a, the threads 21a are engaged with the tooth spaces 8a of the helical spline 8, and the clutch outer member 21 is returned in a forward direction. Then, the retaining ring 27 is fitted in the output shaft 7 to restrict the backward position of the clutch outer member 21. Under the conditions, when the overrunning clutch 20 moves forwardly, front ends of the threads of the clutch outer member 21 hit against the stopper 10 to restrict the forward position of the clutch outer member 21.
The operation of the conventional starting motor will be explained. When a starting switch for an engine of a vehicle etc., an exciting coil (not shown) of the electromagnetic switch 31 is energized to inwardly attract or withdraw the plunger 32 the shift lever 34 is turned by the plunger counterclockwise (refer to FIG. 4) through the hook 33 to move the overrunning clutch 20 forwardly. The forward movement of the overrunning clutch 20 causes the pinion 28 to mate with a ring gear of the engine. The withdrawal of the plunger 32 causes a movable contact (not shown) to get in pressure contact with a pair of fixed contacts (not shown), thereby closing an energizing circuit to the d.c. motor 1. As a result, the armature rotates, the rotation of the armature shaft 2 is transmitted to the pinion 28 through the planetary reduction gear 13 and the overrunning clutch 20 to rotate the ring gear of the engine, thereby starting the engine.
When the engine has started, high speed rotation of the engine drives the pinion 28 in the same direction. However the provision of the overrunning clutch 20 prevents the armature shaft 2 from receiving the driving force.
When the engine has started and the starting switch has been turned off, the plunger 32 of the electromagnetic switch 31 moves forwardly and returns to the forward position to turn the shift lever 34 clockwise in this figure to return it to the home position, causing the overrunning clutch 20 to move backwardly and return to the home position.
In the conventional starting motor as stated above, when the overrunning clutch 20 is at the backward position, the annular engagement groove 21b is located ahead of the retaining ring 27. This means that the distance between the front end of the overrunning clutch 20 and the retaining ring 27 becomes great, which creates a problem in that the external length of the starting motor is enlarged.